Optical fiber fixing method

ABSTRACT

While a ferule  35  or a laser beam is being shifted in an axial direction, the laser beam is applied, thereby forming a plurality of welded portions  55  at the boundary between a coating  33  of an optical fiber  31  and the ferule  35 . A YAG laser in a Q switch pulse mode is used to provide a laser beam. The YAG laser in the Q switch pulse mode is preferably oscillated in a pulse exciting system. The ferule  35  is made of transparent or semi-transparent synthetic resin. The coating  33  of the optical fiber  31  is made of translucent synthetic resin. In this way, an optical fiber fixing method can be provided which can surely fix an optical fiber and a ferule in a shortened time, and minimize the thermal influence on the vicinity of the portion to be processed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to an optical fiber fixing method forfixing a ferule, which is a terminal component for opticalcommunication, and an optical fiber to each other.

[0003] 2. Description of the Related Art

[0004] As well known, a method of connecting optical fibers to eachother is roughly classified into a permanent connection in which theycannot be disconnected after once connected, and a connector splicing inwhich they can be freely disconnected even after once connected. Thepermanent connection is a technique by fusion splicing or bondingsplicing. The connector splicing is to fit connectors (one is a plug,and the other is a receptacle) to each other so that the end surfaces ofoptical fibers are physically spliced to each other.

[0005] The latter connector connection has a disadvantage of greatconnection loss of the optical fiber due to axis displacement, axisinclination, etc., but has an advantage of short splicing time.Therefore, the connector splicing has been widely employed as aconnecting technique for short-distance optical communication, e.g. atechnique of communication devices within a vehicle such as a motor car.

[0006] The optical connector for connector splicing includes an opticalfiber serving as a communication line and a ferule serving as a terminalcomponent. The ferule is employed to position the optical fiber in anaxial direction and a radial direction, and to fix the terminal side ofthe optical fiber. The technique for splicing the optical fiber andferule is implemented in various manners, in particular, in a manner ofusing adhesive.

[0007] An explanation will be given of the method of splicing theoptical fiber and ferule using adhesive. The optical fiber includes afiber wire composed of a core and cladding, and a coating. On the tipside of the optical fiber, the coating is peeled to expose the fiberwire.

[0008] The ferule is formed in a cylindrical shape. The through-holeformed internally has a small diameter portion and a large diameterportion. The small diameter portion has a diameter enough to insert thefiber wire. The large diameter portion has a diameter enough to insertthe coating. The tip of the fiber wire passed into the small diameterportion is ground to be flush with the end surface of the ferule.

[0009] The ferule and optical fiber can be made of various materials,e.g. quartz glass or synthetic resin. Further, the ferule may be made ofmetal or ceramic.

[0010] The optical fiber and ferule are fixed to each other in such amanner that adhesive is applied to the coating of the optical fiber, theoptical fiber is inserted into the ferule and the adhesive is hardened.

[0011] However, the fixing method using the adhesive takes a long timeto heat and harden the adhesive. This presents problems of lowproductivity of the optical connector, of changes in the bondingstrength due to the surface property (surface wettability, surfacecoarseness, etc.) and of low heat resistance. JP-A-11-142688 hasproposed a technique for solving these problems.

[0012] As seen from FIG. 5, by irradiating the end surface 60 a of anoptical fiber 60, inserted in a through-hole 61 a of a ferule 61, with alaser beam 63, the boundary 62 between the ferule 61 and optical fiber60 is molten with thermal energy of the laser beam 63 so that the ferule61 and the optical fiber 60 are fixed to each other.

[0013] However, the conventional fixing method presents the followingproblem to be solved.

[0014] Firstly, since the ferule 61 is irradiated with the laser beam 61from its end surface, the molten area is so small that the fixing cannot be assured. Therefore, if tensile stress acts on the optical fiber60, the optical fiber 60 may come off from the ferule 61.

[0015] Secondly, even when the laser beam 63 is applied from the side ofthe ferule, according to the manner of applying the laser beam 63, thelaser beam 63 is not uniformly applied so that the fixing force is notconstant. Specifically, to some places, the laser beam 63 is stronglyapplied and the fiber wire may be damaged, whereas to other places, thelaser beam 63 is weakly applied and the fiber wire may be insufficientlyheated. The reason why the laser beam 63 is applied strongly or weaklyis that the applying distance of the laser beam 63 varies according toplaces.

[0016] If the applied area becomes large because the laser beam is outof focus, the layer susceptive to thermal influence extends outwardly.In this case, the fiber wire consisting of a core and cladding maygenerate thermal cracks. The layer susceptive to thermal influence canbe narrowed by decreasing the output of the laser beam. However, in thiscase, the heating becomes insufficient so the fixing cannot be assured.

SUMMARY OF THE INVENTION

[0017] In view of the above problems, an object of this invention is toprovide an optical fiber fixing method which can reduce the time takento fix an optical fiber and a ferule, assure the fixing and minimize thethermal influence on the vicinity of the place to be processed.

[0018] In order to attain the above object, there is provided an opticalfiber fixing method for fixing an optical fiber having a coating into acylindrical ferule, characterized by comprising the step of:

[0019] applying a laser beam while either the ferule or laser beam isbeing shifted in an axial direction of the ferule so that a plurality ofwelded portions are formed at the boundary between the coating of theoptical fiber and the ferule.

[0020] In accordance with the configuration, since the optical fiber andferule are fixed to each other using a laser beam, the time taken forfixing can be shortened. Further, since the laser beam is applied whileeither the ferule or the laser beam is being shifted in an axialdirection of the ferule, the welded portions each having a line shapeare formed with the laser beam being in focus, i.e. the power density ofthe laser beam being constant so that the welding area can be increasedand the fixing force between the optical fiber and the ferule can alsoimproved. Furthermore, by narrowing the interval between the adjacentwelded portions, the welding area can be further increased, therebyimproving the fixing force. Therefore, even if the surface of thematerial to be processed is curved, the laser welding can be performedwith the power density being constant.

[0021] In order to the above object, there is also provided an opticalfiber fixing method for fixing an optical fiber having a coating into acylindrical ferule, characterized by comprising the step of:

[0022] applying a laser beam while either the ferule or laser beam isbeing shifted in a direction perpendicular to an axial direction of theferule so that a plurality of welded portions are formed at the boundarybetween the coating of the optical fiber and the ferule.

[0023] In accordance with this configuration, the welded portions eachhaving a line shape can be easily formed without rotating the ferule,thereby improving the workability of fixing between the optical fiberand the ferule.

[0024] In order to attain the above object, there is also provided anoptical fiber fixing method for fixing an optical fiber having a coatinginto a cylindrical ferule, characterized by comprising the step of:

[0025] applying a laser beam while either the ferule or laser beam isbeing rotated about a longitudinal axis of the ferule, so that aplurality of welded portions are formed at the boundary between thecoating of the optical fiber and the ferule.

[0026] In accordance with the above configuration, since the laser beamis applied while either the ferule or the laser beam is being rotated,the welded portions each having an arc shape can be formed with thelaser beam being in focus, i.e. the power density being constant.

[0027] In the optical fiber fixing method, preferably, the laser beam isprovided by a YAG laser in a Q switch pulse mode.

[0028] In accordance with the above configuration, since the laser beamis provided from the YAG laser in the Q switch pulse mode, the highoutput can be acquired for a short time. This prevents the thermalinfluence such as thermal shock from being given to the fiber wireconsisting of a core and cladding.

[0029] In the above optical fiber fixing method, preferably, the YAGlaser is oscillated in a pulse-exciting system.

[0030] In accordance with the above configuration, since the laser beamis excited in the pulse exciting system, the laser welding can beperformed with a shallow welding depth and less influence on theenvironment.

[0031] In any one of the above optical fiber fixing methods, preferably,the ferule is made of transparent or semitransparent synthetic resin,and the coating of the optical fiber is made of opaque synthetic resin.

[0032] In accordance with the above configuration, since the ferule ismade of the transparent or semi-transparent synthetic resin, the laserbeam passes through the ferule. Since the coating is made of the opaquesynthetic resin, the laser beam is absorbed into the coating. Thus, thelaser beam applied from the outside of the ferule is not absorbed by theferule but absorbed by the coating which is to be heated and molten.

[0033] The above and other objects and features will be more apparentfrom the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a diagram showing the basic configuration of a YAG laserprocessing machine employed in an embodiment of the method for fixing anoptical fiber according to this invention;

[0035]FIG. 2 is an exploded perspective view of an optical connectorincluding the optical fiber;

[0036]FIGS. 3A and 3B are views showing the laser-welded states of theoptical fiber and a ferule in which a striped welded portion is formedin an axial direction of the ferule (FIG. 3A) and in which arc shapedwelded portions are formed in a direction perpendicular to the axialdirection of the ferule (FIG. 3A), respectively;

[0037]FIG. 4 is a sectional view of the state where the terminal side ofthe optical fiber is inserted into the ferule fit into an opticaladapter; and

[0038]FIG. 5 is a sectional view showing an example of a conventionaloptical fiber fixing method.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0039] Now referring to the drawings, a detailed explanation will begiven of an embodiment of this invention.

[0040] FIGS. 1 to 4 show an embodiment of an optical fiber fixing methodaccording to this invention.

[0041]FIG. 1 shows a basic configuration of a YAG laser processingmachine 10 which is employed in this embodiment. The YAG laserprocessing machine 10 includes a laser oscillator 11, a processingoptical system 20 and a workpiece system 25 to be processed.

[0042] The basic configuration of the laser oscillator 11 includes atleast one host member (rod) 12, an exciting lamp 13 and a pair of beamcondensing reflecting mirrors 14. The host member 12 is cylindrical andmade of a YAG (yttrium aluminum garnet) crystal doped with Nd(neodymium). The laser output is integer-times as large as the hostmember 12.

[0043] The exciting lamp 13 is a “pumping device” for injecting energyinto the host member 12 and induced-emitting light. A pair of excitinglamps are arranged on both sides of the host member 12. The pumpingformat of the YAG laser includes a continuous-wave (CW) pumping formatand a pulse exciting format. The CW pumping employs a Kr arc lamp. Thepulse pumping employs a Xe flash lamp. Both pumping lamps pump(side-pump) the host member 12 from the side.

[0044] In the CW pumping, the pumping is continuously carried out toprovide the laser beam 28 due to the CW oscillation. In the pulsepumping, the pumping is intermittently carried out to provide the laserbeam 28 due to the pulse oscillation. In short, the YAG laser can beemployed for both CW oscillation based on the CW pumping and the pulseoscillation based on the pulse pumping.

[0045] The beam condensing reflecting mirror 14 is provided around thehost member 12 and pumping lamp 13. The beam condensing reflectingmirror 14 serves to inject effectively the laser beam from the pumpinglamp 13 into the host member 12, and amplify the bumped laser beam.

[0046] On an extending line of the host member 12, between the pair ofbeam condensing reflecting mirrors 14 and 14 are arranged a modeselector 16, Q switch 17 and a beam shutter 18. The mode selector 16serves to select the strength distribution (transverse mode) of thelaser beam 28. A stable mode of the strength distribution is a Gaussianmode (TEM₀₀) in which the beam strength becomes low at a fartherposition from the optical axis. An unstable mode of the strengthdistribution is a multimode. The multimode provides a high output in theGaussian mode. The laser beam 28 in the Gaussian has an advantage ofsuitableness of processing at high precision.

[0047] The multimode and Gaussian mode have a continuous-wave (CW)pumping and a pulse pumping each. In the multimode, the CW pumping inthe multimode provides a high output of several tens of W to 2 KW. Thepulse pumping provides an output of several KWs or higher. On the otherhand, in the Gaussian mode, the CW pumping provides an output of 6 to 10W. The pulse pumping provides an output of several Ws.

[0048] The beam shutter 18 is a safety device for emergency cut-out oflaser oscillation. Therefore, normally, the beam shutter 18 is notnormally turned on/off to operate the YAG laser processing machine 10.

[0049] As described above, the oscillation mode of the laser beam 28 hasa Q switch pulse as well as the multimode and Gaussian mode (singlemode). The Q switch pulse is a technique for acquiring a peak outputwith a high output and a narrow time width by performing pumping in astate with the loss of the laser oscillator 11 increased to accumulateenergy at an exciting level and reducing the loss at a convenient time.This invention is characterized in that the Q switch pulse is employedfor the laser beam 28.

[0050] The Q switch pulse laser is a laser which is operated so that ashort pulse can be repeatedly oscillated at a high speed. Unlike thepulse pumping system, the Q switch pulse does not oscillate the laserrepeatedly by turning on/off. The Q switch, therefore, can oscillate thelaser at a high repetition speed on the order of kHz.

[0051] An explanation will be given of the theory of the Q switchoperation. The Q switch operation is carried out by the Q switch 17(optical shutter) which is incorporated in the laser oscillator 11. Whenthe Q switch 17 turns on/off (switches) the pumping lamp 13 for CWpumping and pulse pumping at a high speed, the laser beam 28 with ashort pulse and high peak output is oscillated.

[0052] The Q switch 17 includes an AO (acoustic optics) Q switch and anEO (electric optics) Q switch. The AO-Q switch is a switch for CWpumping. In this system, with a laser element provided within the laseroscillator 11, an ultrasonic wave is turned on/off to provide the laserbeam 28 to several tens of kHz.

[0053] The repetitive frequency of the Q switch 17 can be set at 0.1-30kHz. However, according to the output characteristic of the Q switch 17,since the peak output is lowered when the repetitive frequency is toolow or too high, in this embodiment, the repetitive frequency is set at2-10 Hz.

[0054] The EO-Q system serves as a shutter together with a deflectingelement by deflecting a deflecting direction by external application ofan electric field. The EO-Q switch is employed for a Q switch pulse at ahigh speed.

[0055] The basic configuration of the processing optical system 20includes a beam bender 21 and a beam positioner (not shown) Where thelaser oscillator 11 and a workpiece 27 are held horizontally, the beambender 21 serves to cause the laser beam 28 to be vertically incident onthe workpiece 27. The beam bender 21 is provided with a mirror 21 a anda condensing lens 21 b. The mirror 21 a serves to change the opticalpath of the laser beam 28 oscillated by the laser oscillator 11. Thecondensing lens 21 b incorporated within a nozzle 21 a serves tocondense the laser beam 28.

[0056] The beam bender 21 is provided with a fine adjusting mechanism(not shown) which can alter the positions of the workpiece 27 andcondensing lens 21 b. For this reason, the laser beam 28 is uniformlyapplied to the ferule having a three-dimensional curve.

[0057] The basis configuration of the workpiece system 25 includes aworktable 26 and a driving mechanism (not shown) for driving theworktable 26 in two-axes directions. The driving mechanism serves todetermine the positional relationship between the processing opticalsystem 20 and the workpiece 25. The driving mechanism shifts theworktable 26 in any direction by the driving mechanism so that the laserbeam 28 apparently scan on the workpiece 27. Incidentally, with theworktable 26 secured, the processing optical system 20 may be shifted inthe two-axes directions by an NC controller.

[0058]FIG. 2 is an exploded perspective view of an optical connector 30.The optical connector 30 includes an optical fiber 31, a ferule 35, anoptical adapter 40 and an optical adapter cover 50. The respectivecomponents will be explained in this order.

[0059] The optical fiber 31 includes a fiber wire 32, an inner sheath(also referred to as a coating) 33 for covering the fiber wire 32, andan outer sheath for sheathing the outside of the inner sheath. The fiberwire 32 is a “plastic fiber wire” made of synthetic resin. For example,PMMA (poly methyl methacrylate) or polycarbonate (PC) having heatresistance is employed as the material of a core and fluororesin and thelike are employed as the material for a cladding.

[0060] The core located centrally in the fiber wire 32 is a waveguide(transmission line) for transmitting an optical signal. The cladding islocated outside the core and serves to confine light within the core.The cladding is made of a material having a small refractive index.Therefore, the optical signal repeats to be reflected on the boundarybetween the core and cladding so that it is confined within the core.

[0061] The inner sheath 33 and the outer sheath 34 are made of syntheticresin having insulation and fire resistance, such as polyethylene, vinylchloride, nylon, etc.

[0062] The inner sheath 33 and outer sheath 34 are peeled successivelyfrom the tip of the optical fiber 31 so that the fiber wire 32 isexposed to a prescribed length. The inner sheath 33 is exposed on thetip side of the outer sheath 34 to a prescribed length. The inner sheath33 is heated by the laser beam 28 and fixed.

[0063] The ferule 35 is a “plastic ferule” which is made of atransparent or semi-transparent synthetic resin capable of transmittingthe laser beam. The ferule 35 is a stepped cylinder which includes asmall-diameter portion 36 which accommodates the fiber wire 32 in athrough-hole 35 a (FIG. 4) and a large-diameter portion 37 which iscontinuous to the small-diameter portion 36 which accommodates the innersheath 33 in the through-hole 35 a. The fiber wire 32 is inserted in thethrough-hole 35 a so that it is exposed from the end of thesmall-diameter portion 36. The fiber wire 32 is ground together with theferule 35 so that the end face is exposed.

[0064] The body of the large-diameter portion 37 has a first flange 38and a second flange 39 which are ring-shaped, respectively. The firstflange 38 is formed in the middle of the large-diameter portion 37, andthe second flange 39 is formed at the end of the large-diameter portion37.

[0065] The optical adaptor 40 is made of synthetic resin, and includestwo cylinders 41, 41 each having an external square shape, which areintegrally arranged side by side. These two cylinders 41, 41 aresymmetrical. Each cylinder 41 includes an insertion inlet 42, anaccommodating chamber 43 (FIG. 4) and a connection inlet 44 (FIG. 4).

[0066] The insertion inlet 42 is a circular through-hole formed forinserting the terminal side of the optical fiber 31. The insertion inlet42 is formed in the end face of the one side in a longitudinal directionof the optical adaptor 40. The diameter of the insertion inlet 42 ismade slightly larger than those of the first and second flange 38 and39.

[0067] The accommodating chamber 43 is made longer than the ferule 35 sothat the accommodated ferule 35 does not protrude from the connectioninlet 44. This intends to prevent the respective tips of the ferule 35and the optical fiber 31 from being damaged or broken. The accommodatingchamber 43 has diameters equal to those of the insertion inlet 42 andconnection inlet 44, and has a ring-shaped stopper 45 (FIG. 4) whichprotrudes inwardly and formed circumferentially in the middle. Thestopper 45 is in contact with the first flange 38 of the ferule 35 sothat the ferule 35 is positioned in the longitudinal direction.

[0068] The connection inlet 44 is formed on the other end face of theoptical adapter 40 in the longitudinal direction. The connection inlet44 is a place into which a complementary optical connector (not shown)is fit, and is formed in a shape of a circular through-hole.

[0069] The optical adapter 40 has a securing portion 46 formed at anupper wall 40 a and an engagement hole 47 formed at a lower wall 40 b(not shown). The securing portion 46 is a flexible securing piece formedon the side of the insertion inlet 42 with respect to the center of theoptical adapter 40. The securing portion 46 is engaged with the firstflange 38 of the ferule 35 to prevent the ferule 35 from coming off fromthe rear.

[0070] The engagement hole 47 is communicated with the accommodatingchamber 43. A holder 49, which is inserted in the engagement hole 47, isengaged with the first flange 38 of the ferule 35 to secure the ferule35 doubly.

[0071] The optical adaptor cover 50, which is made of synthetic resin,is formed in the form of a frame so as to receive the optical adaptor40. The optical adaptor cover 50 is composed of a deep wall and acircumferential wall 51. The circumferential wall 51 is composed of anupper wall 51 a, a low wall 51 b and side walls 51 c, 51 c (only one isshown).

[0072] In the lower wall 51 b of the optical adaptor cover 50, anengagement hole 53 is formed so as to correspond to the holder 49. Theengagement hole 53 has a size approximately equal to the engagement hole47 (FIG. 4) of the optical adaptor 40. When the holder 49 is insertedinto the engagement hole 53, the holder 49 passes through the engagementhole 53 and is engaged with the first flange 38 of the ferule 35.

[0073]FIG. 4 shows the state where the terminal side of the opticalfiber 31 is inserted in the ferule 35 fit in the optical adaptor 40. Theoptical fiber 31 is inserted from the rear end of the ferule 35 and theouter sheath 34 is engaged with the end of the second flange 39. Thus,the optical fiber 31 is positioned in the longitudinal direction.

[0074] The fiber wire thus inserted is brought into intimate contactwith the inner wall of the through-hole 35 so that its optical axis isaccurately positioned radially so as to be free from no inclination.

[0075] The ferule 35 is longitudinally positioned in contact with thestopper 45 of the optical adaptor 40. The first flange 38 of the ferule35 is secured by the securing portion 46 so that the ferule 35 does notcome off from the direction opposite to that of insertion.

[0076]FIGS. 3A and 3B show the state where the optical fiber 31 andferule 35 have been laser-welded by the YAG laser processing machine 10,respectively. Specifically, FIG. 3A shows the case where welded portions55 composed of lines has been welded in an axial direction X of theferule 35. FIG. 3B shows the case where welded portions composed of arcsin a direction Y perpendicular to the axial direction. In both cases,the welded portions 55, 56 are formed at the boundary between the innersheath 33 and ferule 35 so that the fiber wire 32 is not thermallyinfluenced.

[0077] The welded portion 55 shown in FIG. 3A can be formed, forexample, by shifting the fixed laser beam 28 in the axial direction X ofthe ferule 35. The plurality of welded portions 55 can be formed byshifting the ferule 35 with a prescribed pitch in the direction Yperpendicular to the axial direction. Otherwise, with the ferule 35being fixed, the laser beam 28 may be shifted.

[0078] The welded portion 56 shown in FIG. 3B can be formed, forexample, by axially rotating the fixed laser beam 28. The plurality ofwelded portions 56 can be formed by shifting the ferule 35 with aprescribed pitch in the axial direction X. Otherwise, with the ferule 35being fixed, the laser beam 28 may be shifted. Otherwise, with the laserbeam 28 being fixed, the laser 28 may be rotated around the ferule 35.

[0079] In this way, in any case, since the laser beam 28 being in focus,i.e. power density is constant, the welded portions 55, 56 are formed,even if the surface to be processed is curved, the optical fiber 31 andferule 35 can be surely laser-welded to each other.

[0080] Using the Q switch pulse at the frequency of 2-10 kHz, the laserbeam 28 is applied from the side of the ferule 35 to melt the innersheath 33 of the optical fiber 31 so that the inner sheath 33 and theferule 35 are fixed to each other. The laser beam 28 can be applied inany condition, but in this embodiment, the laser welding has beencarried out with the laser output of 17-22A and at the speed (rotatingspeed in the case of FIG. 3B) of scanning the laser beam 28 of0.002-0.03 m/s.

[0081] The frequency, laser output and scanning speed of the laser beamin the Q switch pulse mode can vary according to the material, shape andsize of the ferule 35, material of the optical fiber 31 and thethickness of the inner sheath 33. However, the application condition ofthe Q switch pulse has been set so that the optical fiber 31 and theferule 35 can be fixed without giving thermal shock to the fiber wire32.

[0082] The use of the Q switch pulse intends to provide a peak outputwith a high output and narrow time width by oscillating a short pulse ata high repetitive speed. This can narrow the thermally influenced layerin the vicinity of the welded portion, and hence can prevent the fiberwire 32 from being damaged. The Q switch pulse can preferably excite thepulse which provides a shallower melting depth and less thermalinfluence on the environment.

[0083] As shown, the plurality of welded portions 55, 56 are formed inorder to increase the welding area and improve the fixing force betweenthe optical fiber 31 and the ferule 35. Although the interval betweenthe adjacent welded portions is not limited, narrowing the intervalimproves the fixing force.

[0084] Since the respective welded portions 55, 56 are formed with thelaser beam 28 being in focus, i.e. the laser beam 28 is applied with thepower density being constant, even if the outer surface of the opticalfiber 31 is curved, the optical fiber 31 and ferule 35 can be surelysecured to each other.

[0085] The use of the YAG laser serving as the solid laser for the laserbeam 28 intends to make the welding by the laser beam with a shortwavelength, thereby performing the accurate processing for a short timewithout giving thermal influence on the fiber wire 31.

[0086] In this way, in accordance with this embodiment, since theoptical fiber 31 and ferule 35 are fixed using the laser beam 28, thefixing time can be shortened to improve the productivity as comparedwith the case of fixing using adhesive. Further, since the laser beam 28is applied while either the ferule 35 or the laser beam 28 is beingshifted, the welded portions 55 and 56 each having a line or arc shapeare formed with the power density being constant, and the welded areascan be increased, thereby improving the fixing force between the opticalfiber 31 and the ferule 35.

[0087] This invention should not be limited to this embodiment, but thelaser welding can be realized in the following manner. The laser beam 28is applied while either the ferule 35 or the laser beam 28 is beingshifted in the direction Y perpendicular to the axial direction. Then,after the ferule 35 is turned over by 180°, the laser beam 28 is appliedagain while either the ferule 35 or the laser beam 28 is being shiftedin the direction perpendicular to the axial direction. If the sufficientfixing strength can be obtained on the one side of the ferule 35, it isnot necessary to turn over the ferule 35 by 180°. In accordance withthis technique, since the welded portions each being in a line shape canbe easily formed in the direction Y perpendicular to the axialdirection, the configuration for the processing system does not becomecomplicate, thereby improving the workability of fixing between theoptical fiber 31 and the ferule 35.

[0088] Incidentally, the contents of Japanese Patent Appln. No.02-209513 filed on Jul. 18, 2002 are hereby incorporated by reference.

What is claimed is:
 1. An optical fiber fixing method for fixing anoptical fiber having a coating into a cylindrical ferule, comprising thestep of: applying a laser beam while either said ferule or laser beam isbeing shifted in an axial direction of the ferule so that a plurality ofwelded portions are formed at the boundary between the coating of saidoptical fiber and said ferule.
 2. An optical fiber fixing method forfixing an optical fiber having a coating into a cylindrical ferule,comprising the step of: applying a laser beam while either said feruleor laser beam is being shifted in a direction perpendicular to an axialdirection of the ferule so that a plurality of welded portions areformed at the boundary between the coating of said optical fiber andsaid ferule.
 3. An optical fiber fixing method for fixing an opticalfiber having a coating into a cylindrical ferule, comprising the stepof: applying a laser beam while either said ferule or laser beam isbeing rotated about a longitudinal axis of the ferule, so that aplurality of welded portions are formed at the boundary between thecoating of said optical fiber and said ferule.
 4. An optical fiberfixing method according to any one of claims 1 to 3, wherein said laserbeam is provided by a YAG laser in a Q switch pulse mode.
 5. An opticalfiber fixing method according to claim 4, wherein said YAG laser isoscillated in a pulse-exciting system.
 6. An optical fiber fixing methodaccording to any one of claims 1 to 5, wherein said ferule is made oftransparent or semitransparent synthetic resin, and said coating of theoptical fiber is made of opaque synthetic resin.